Microwave ovens are well-known for the rapid volumetric heating of food. A common problem encountered with microwave heating is the lack of uniformity of heating particularly on the edges and corners of solids.
In large scale continuous food production, uniformity of heating and the control of temperature is very important, particularly where the food is to be processed to kill bacteria in, for example, pasteurisation or sterilisation treatment. Commonly individual meals in boxes (chill foods) or rectangular blocks of wrapped food product are passed through a microwave processing oven on a conveyor belt which is transparent to the microwaves.
The present invention seeks to provide a means of heating articles, such as food products, so that there is substantially uniform heating. The invention also seeks to enable a train of articles, such as discretely wrapped solids, to be subjected to microwave energy concentrated in the discrete articles and not in the gaps within the article train. The invention also seeks inherently to control the energy dissipated in the leading and trailing edges of the solid articles in the train so as to provide substantially uniform heating throughout the article.
The invention therefore seeks to provide a method and means for controlling the temperature, for achieving substantially uniform heat distribution, and for controlling the rate of rise of temperature in the article without unnecessary energy loss between articles in a train of articles to be processed.